Examination of the eye is widely performed for early diagnosis and treatment of lifestyle diseases and diseases which are primary causes of loss of eyesight. The scanning laser ophthalmoscope (SLO), which is an ophthalmological apparatus that employs the principle of confocal laser scanning microscopy, performs raster scanning of a laser, which is measurement light, over the fundus, and acquires a high-resolution planar image from the intensity of returning light at high speed. Detecting only light that has passed through an aperture (pinhole) enables an image to be formed just using returning light of a particular depth position, and images with higher contrast than fundus cameras and the like can be acquired. An apparatus which images such a planar image will hereinafter be referred to as an SLO apparatus, and the planar image to as an SLO image.
In recent years, increased beam diameter of measurement light in SLO apparatuses has enabled acquisition of SLO images of the retina, with improved horizontal resolution. However, the increased beam diameter of the measurement light has led to a problem of deterioration the sound-to-noise (SIN) ratio and the resolution of the SLO image during acquisition of SLO images of the retina, due to aberration of the eye being examined. An adaptive optic SLO apparatus has been developed to solve this problem. The adaptive optic SLO apparatus has an adaptive optic system that measures aberration of the eye being examined in real time using a wavefront sensor, and corrects aberration occurring in the eye being examined with regard to the measurement light and the returning light thereof using a wavefront correction device. This enables SLO images with high horizontal resolution (high-magnification image) to be acquired.
Such a high horizontal resolution SLO image can be acquired as a moving image. In order to noninvasively observe hemodynamics, for example, retinal blood vessels are extracted from each frame, and the moving speed of blood cells through capillaries and so forth is measured. Also, in order to evaluate the relation with visual function using an SLO image, photoreceptors P are detected, and the density distribution and array of the photoreceptors P are calculated. FIG. 6B illustrates an example of a high horizontal resolution SLO image. The photoreceptors P, a low-luminance region Q corresponding to the position of capillaries, and a high-luminance region W corresponding to the position of a white blood cell, can be observed. In a case of observing photoreceptors P in the SLO image, the focus position is set nearby the outer layer of the retina (B5 in FIG. 6A) to take a SLO image such as in FIG. 6B. On the other hand, there are retinal blood vessels and capillaries that have branched running through the inner layers of the retina (B2 through B4 in FIG. 6A). Acquiring an adaptive optics SLO image with the focus position set in the inner lavers of the retina enables the retinal blood vessel walls, which are fine structures relating to retinal blood vessels, to be directly observed.
However, confocal images taken of the inner layers of the retina have intense noise signals due to the influence of light reflecting from the nerve fiber layer, and there have been cases where observing blood vessel walls and detection of wall boundaries has been difficult. Accordingly, as of recent, techniques have come into use using observation of non-confocal images obtained by acquiring scattered light, by changing the diameter, shape, and position of a pinhole on the near side of the light receiving portion (NPL 1). Non-confocal images have a great depth of focus, so objects that have unevenness in the depth direction, such as blood vessels can be easily observed, and also noise is reduced since reflected light from the nerve fiber layer is not readily directly received. While observation of photoreceptors at the outer layers of the retina has primarily involved imaging confocal images of the outer segment of photoreceptors, it has been found that the unevenness of the inner segment of photoreceptors can be imaged in non-confocal images (NPL 2). Although a region where an initial lesion has damaged the outer segment but the inner segment has survived is imaged as a black defect area in confocal images (Dc5 in FIG. 6K), this can be observed as a region where high-luminance granular objects exist in non-confocal images (Dn5 in FIG. 6L). NPL 1 discloses technology for acquiring non-confocal images of retinal blood vessels using an adaptive optics SLO apparatus, while NPL 2 discloses technology for acquiring both confocal images and non-confocal images at the same time using an adaptive optics SLO apparatus. Further, technology for effectively taking tomographic images of the eye is disclosed in PTL 1.